1. Field of the Invention
The present invention relates to self-crosslinking aqueous polymer, e.g., polystyrene-butadiene, dispersions for consolidating bituminizable base materials such as, for example, bituminized roofing mats and also to the nonwovens consolidated using these polymer dispersions.
2. Background of the Invention
EP-A-0438 284 describes an aqueous polymer emulsion having a low free-formaldehyde content, which is achieved by using N-methylolacrylamide as formaldehyde scavenger. The compound is used for crosslinking polyvinyl acetate and vinyl acetate-styrene dispersions.
WO 97/32930 describes an aqueous dispersion for coating textiles which is composed of a hydrophilic polyurethane (PU) and a copolymer of styrene, butadiene and further copolymerizable monomers. These PU dispersions are used for coating roofing mats.
DE-A 40 29 733 describes bound nonwovens comprising a binder composed of a dispersion prepared by polymerization of a conjugated diene, and xcex1,xcex2-unsaturated mono- or dicarboxylic acid and hydroxyl containing olefinic monomers.
U.S. Pat. No. 4,125,663 discloses a process for the production of bound nonwovens using a polymer dispersion comprising melamine/formaldehyde resins as crosslinkers.
Bituminized roofing mats are produced by saturating and/or coating a base material with bitumen. The formerly used base materials composed of cardboard failed to keep pace with increasing performance expectations and have been superseded by raw felt, woven jute fabric, glass mats, mixed glass fiber cloth and especially by polyester spunbondeds and also polyester staple fiber webs. Such nonwovens, consolidated with dispersion binder, for example, have to meet the following performance requirements in bituminization and end use:
Low Extensibility at 160 to 200xc2x0 C. Under High Tensile Stress, High Mechanical Strength
The reinforcing construction of bound nonwoven should extend little if at all under the production conditions of bitumen impregnation and/or coating. 1% extension must not be exceeded at 160 to 200xc2x0 C. and the high tensile stresses due to the highly viscous bitumen and the high production speeds. A higher extensibility would cause stresses to be frozen into the roofing mat as it cooled down and was wound up, which would become rereleased on renewed heating, for example in the course of the welding of the seams or in the event of strong insolation. This would lead to cracks in the roof membrane. The low-extensibility requirement applies longitudinally, transversely and diagonally.
Good Adhesion to Bitumen
Low Sensitivity to Water, High Watertightness
If the bound nonwovens (fiber material, binder) are not sufficiently hydrophobic, the wicking effect of individual filaments may cause water to ingress at the points of intersection of the roofing mats. This leads to separation between the bitumen and the bound nonwoven or to frost damage.
Flexibility and Extensibility of Construction in End Use
Owing to temperature fluctuations in end use (xe2x88x9240xc2x0 C. to +80xc2x0 C.) and differences in the expansion coefficients of various building materials, the entire roofing mat is subject to relatively large dimensional changes. Excessive stiffness and inflexibility of the overall construction gives rise to fine cracks which, combined with moisture and low temperatures, lead to the destruction of the roofing mat. It is therefore urgently necessary that not only the bitumen but also the reinforcement of bound nonwoven remain flexible at the use temperature.
The present invention is based on the surprising discovery that polymers of aromatic vinyl compounds and conjugated dienes, e.g., styrene-butadienes, copolymerized with compounds having self-crosslinking groups are useful for impregnating nonwovens. The end products obtained have the required dimensional stability at high temperatures and are substantially insensitive to water. Room temperature mechanical properties are similar to those of standard systems.
Accordingly, the present invention provides self-crosslinking aqueous polymer dispersions for consolidating bituminizable nonwovens, composed of the following polymerized monomer units:
1) 20 to 55 parts, based on the dry mass of the disperse phase, of at least one conjugated diene,
2) 30 to 80 parts, based on the dry mass of the disperse phase, of at least one copolymerizable aromatic vinyl compound,
3) 0.1 to 10 parts, based on the dry mass of the disperse phase, of at least one polymerizable organic carboxylic acid and/or anhydride,
4) 1 to 10 parts of at least one crosslinker,
5) 0 to 20 parts, based on the dry mass of the disperse phase, of at least one derivative of an xcex1,xcex2-unsaturated carboxylic acid.
A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description.
A particularly useful component 1) is 1,3-butadiene. Other 1,3-dienes may be used as well, for example isoprene, chloroisoprene or 2,3-dimethylbutadiene. Butadiene is preferred.
The preferred component 2) is styrene. Other aromatic vinyls may likewise be used, for example methylstyrene or styrene carboxylic acids.
Useful copolymerizable organic carboxylic acids (component 3) include, for example, acrylic acid, methacrylic acid or itaconic acid, used alone or mixed. Maleic acid, fumaric acid, maleic anhydride and fumaric anhydride may also be used. Acrylic acid and/or methacrylic acid are preferred.
The crosslinker (component 4) is in principle an acrylamide or a methacrylamide. The following compounds are preferred: N-methylolacrylamide, N-methoxymethylacrylamide, N-hydroxymethylacrylamide, N-methylolmethacrylamide, N-methoxymethylmethacrylamide and N-hydroxymethylmethacrylamide.
Useful derivatives of xcex1,xcex2-unsaturated carboxylic acids (component 5) include the following compounds: acrylamide, methacrylamide, acrylonitrile and methacrylonitrile.
It is further possible to use the hereinbelow described mixtures of self crosslinking dispersions for consolidating bituminizable nonwovens.
By blending xe2x80x9csoftxe2x80x9d and xe2x80x9chardxe2x80x9d types it is thus possible to freely select different nonwoven application properties, e.g., pliability.
A hard styrene-butadiene rubber (SBR) type, for example, has the following composition: 60% of styrene, 28% of butadiene, 8% of acrylonitrile, 2% of acid, 4% of crosslinker; a soft SBR type, for example, has the following composition: 35% of styrene, 42% of butadiene, 10% of acrylonitrile, 7% of acrylamide, 2% of acid, 4% of crosslinker.
In general, mixing ratios for soft component: hard component are chosen between 7:3 and 0:10.
Preference is given to mixtures between the soft component: hard component mixing ratios of 5:5 to 1:9, particularly 3:7 to 2:8.
The inventive dispersions for consolidating nonwovens may also comprise auxiliary and additive substances, for example anionic emulsifiers, nonionic emulsifiers, aging inhibitors, biocides, defoamers, pH buffers, and complexing agents.
The present invention also provides consolidated nonwovens consolidated using a self-crosslinking aqueous polymer dispersion, composed of the following polymerized monomer units:
1) 20 to 55 parts, based on the dry mass of the disperse phase, of at least one conjugated diene,
2) 30 to 80 parts, based on the dry mass of the disperse phase, of at least one copolymerizable aromatic vinyl compound,
3) 0.1 to 10 parts, based on the dry mass of the disperse phase, of at least one polymerizable organic carboxylic acid and/or anhydride,
4) 1 to 10 parts of at least one crosslinker,
5) 0 to 20 parts, based on the dry mass of the disperse phase, of at least one derivative of an xcex1,xcex2-unsaturated carboxylic acid.
Nonwovens that may be used in the present invention include all known nonwovens, for example nonwovens composed of glass, polymers and natural products and also their hybrid constructions, especially from raw felt, woven jute fabric, glass mat, mixed glass fiber cloth, polyamide and polyester. Spunbonded nonwovens and staple fiber nonwovens are preferred. Polyester spunbondeds and polyester staple fiber webs are particularly preferred. The nonwovens used are readied for this use in a conventional manner, i.e. needled or heat-set. The nonwovens generally have a weight of 20-350 g/m2, preferably 100-250 g/m2.
The components 1) to 5) and further, auxiliary and additive substances are present as described above.